For the UV LED lens packaging, quartz glass has high transmittance (up to 95%); the next highest is silica gel (about 90%); the ultraviolet light transmittance of epoxy resin drops dramatically as the wavelength becomes shorter. The glass material requires extremely high temperature during the thermal process and therefore is not suitable for epitaxy packaging but for lens packaging. In order to have a packaging structure of high luminous efficacy and high reliability, the packaging gels and lens materials must select those having the characteristics of high UV light transmittance, good refractive index, high resistance to UV light, yellowing proof, high temperature resistance capability and good thermal stress. As the epitaxy technologies of LED progresses and matures, LEDs can increasingly meet the demand of diverse applications. Among various applications, owing to the characteristics of a point source of light, optical lenses must be used in order to obtain ideal light types. It is especially true in the application areas of high power LEDs. Before the lighting components of high power LEDs can actually become lighting products, the components generally need to undergo two optical designs. When the LED chips are packaged into LED photoelectric components, the first optical design is applied to solve the issues of light emitting angle, luminous intensity, luminous flux, luminous intensity distribution, range and distribution of color temperature. This is the first optical design. The secondary optical design focuses on the high power LED lighting. Generally a high power LED has a first optical lens with a light emitting angle of about 120°. The secondary optical design is to let the light that has been processed by the first optical lens pass through another optical lens to change the optical features of light. The goal of the first optical design is to maximize the light abstracting volume emitted by the LED chips; the goal of the secondary optical design is to adjust the light emitted from the completely integrated lighting device to meet the design requirements. Through the coordination of highly effective secondary optical lens, the deficiency in brightness, light emitting angle and uniform illuminance of the LED light source can be compensated in order to reduce the number of LED lights used.
The concept of nano structures has been widely applied to the upstream and downstream processes of the LED manufacturing. The main concept is that when light encounters the nano structure, the complete reflectivity of light is interfered by the shape of the nano structure, resulting in diffusion or reflection. In the upstream process of crystallite manufacturing, the nano structure patterned sapphire substrate can increase the light abstracting efficiency and reduce the epitaxy defects. In the downstream process of packaging, in order to cope with LED light apparatuses in the batwing type or concentrating type light applications, currently the international manufacturers mostly adopt the nano structure light diffuser films or the lens with nano structures of the secondary optical design. The manufacturing process of the nano structure light diffuser films generally creates V-shape cuts on an optical grade polymethylmethacrylate (PMMA) substrates. By changing the angle, size, and arrangement of the V-shape cuts to adjust and control the direction and uniformity of the emitted light, and obtain the effect of collimated light, contracted light, or diffused light according to different applications. In order to solve the problem of poor uniformity of the point source of LED light, the conventional method is to add diffusing particles in the PMMA thin films to increase the probability of light scattering. In addition, adding specially designed nano structure diffusing thin films, the emitting angle and uniformity of the LED light source can be controlled and adjusted within the ranges of applications. However, the disadvantage of such nano structure packaging of the secondary optical design is that the size is too huge.
In general, during the packaging process of the LED, a first optical design is applied. The standard lens is a conical lens. Majority of these lenses rely on total internal refection (TIR); thus these lenses are also called TIR lenses. A TIR lens has a design of axial symmetry to provide an excellent circular facula, so that not only a plurality of LEDs can be assembled into an array lens, but also a single LED with a support frame added is easy to be installed and adjust the light. If the requirement is a light source with uniform faculae, it can not be achieved simply by relying on the first optical design. Thus, a secondary optical design is required. Therefore, a light cover with a special structure or a secondary lens is designed for the applications in order to make the light emitted by LEDs to be focused more uniformly. On the other hand, by applying the special structure, the size of the conventional light focusing structure can be reduced to much smaller. Nevertheless, the special structure in the design of the light cover or the secondary lens makes the production process relatively complicated and requires the use of injection molding to increase the production efficiency. However, materials generally used in the injection molding are not suitable for the use of short wave light. Light of short wave, such as ultraviolet light, will cause damages to the materials. Therefore, light covers or secondary lenses in the secondary optical design will deteriorate and become brittle gradually as the usage time increases.
Therefore, currently the industry needs a method of producing secondary lens with hollow nano structures for uniform illuminance in order to solve the aforementioned poor uniformity problems of the point source of LED light and to enhance the characteristics of the secondary lens in high resistance to ultraviolet light, yellowing proof, and lifetime durability. The aforementioned method of the present invention replaces the materials of the special structure used in the light covers or secondary lens and simplifies the structure production process as an effective technology, thus to produce secondary lenses with hollow nano structures that are less expensive with a better scattering effect and can uniform faculae patterns significantly.